Modern semiconductor fabricating equipments or various types of assembling machines used in years are needed to meet a diversity of anticipated design specifications of more miniaturization, and making it possible to work with high speed, high acceleration/deceleration, fast response, high position-control, and so on. Correspondingly, the same sort of design specifications as stated earlier is also required in the component placement systems such as the pick-and-place machines and pick-and-insert machines, which is envisaged carrying out a sequence of picking up a workpiece including a part, component and so on, transferring the workpiece to a desired placement position, and placing the workpiece on the desired position with high precision.
In Japanese Laid-Open Patent Application No. 2006-238 540, or reference 1, which is a commonly-assigned senior application, there is disclosed an example of the sliding system with an onboard linear motor, which is used for pick-and-place machines. The sliding system is intended to work in standing posture that is classified as a vertical sliding system. The prior sliding system has a stationary bed of flat configuration having a vertical front surface and a vertical rear surface, an X-table allowed to travel relatively to the bed in an X-direction lying in the horizontal by an X-linear motor, and a Z-table allowed to travel relatively to the X-table in a Z-direction lying in the vertical, especially, perpendicularly to the horizontal by a Z-linear motor. With the sliding system constructed as stated earlier, the Z-table and the X-table are both laid on any one vertical surface of the bed so as not to overlap one another to make the sliding system itself slim in thickness and compact in construction. All of the bed, X-table and the Z-table are made of magnetic material, especially steel and, therefore, the X-table functions as a magnetic yoke of the X-linear motor while the Z-table serves as a winding yoke of the Z-linear motor.
Another prior sliding device with onboard moving-magnet linear motor is disclosed in, for example Japanese Laid-Open Patent Application No. 2007-300 759, or reference 2 which is assigned to the same assignee as the present disclosure. The prior sliding device has a field magnet secured on the underside of a table and composed of magnet strips juxtaposed in an array that their polarities alternate in an sliding direction of the table, and an armature assembly having a plurality of armature windings lying on an upper side of the bed facing on the table in opposition to the field magnet, the armature windings being each composed of a coreless coil formed in a flat rectangular shape. With the armature assembly, more especially, the armature windings are laid on a circuit board secured on the upper surface of the bed. A protective sheet of thin film is applied to shield the exposed surfaces of the armature windings opposite to the circuit board, and then a molding of adhesive material of bonding agent to make the armature windings integral with the circuit board. Some instruments and components including limit sensors, before-origin sensors, and so on are dislodged from the sliding device, and therefore the armature assembly has only the armature windings and the associated wirings. On the underneath of the table, moreover, there is placed none of end plates, auxiliary magnets, sensor magnets, origin marks, and so on which have been so far installed with accompanying the field magnets. Though this prior construction as stated earlier makes it possible to render the sliding device compact in construction and simple in system design, the armature windings and the field magnets couldn't get out of becoming more massive than ever to increase the propelling force or thrust in the sliding device.
In the prior sliding system with an onboard linear motor adapted to be used for pick-and-place machines, recited with reference to the first cited prior art, the Z-table is connected with the X-table so as to be able to move in both the X-direction and the Z-direction with respect to the bed. With the prior sliding system constructed as stated earlier, however, the difficulty is that even if the propelling power of the onboard X-linear motor and Z-linear motor is envisaged increasing to raise the working efficiency, that is, takt time or cycle time, the sliding system itself would become more massive because the X-table loaded with the Z-table would become increasingly weighty. Thus, it remains a major challenge to maintain the property of high working-efficiency, or high productivity with short takt-time without becoming larger or bulkier in construction.
The sliding system with an onboard linear motor recited in the second cited prior art would teach or suggest that the X-Y sliding system free to move both in X-direction and in Y-direction could be provided easily by just connection of a pair of sliding devices in perpendicular to each other. Nevertheless, the pick-and-place machines need the sliding system less in takt time or cycle time. To this end, it remains a challenge to make the movable components or parts less in weight.